1. Field of the Invention
The invention relates to a combination of antenna having at least two individual antennae, whose output signals are combined.
2. Description of the Related Technology
Antenna combinations of this type are generally known and for example described in the book Meindke-Gundlach "Taschenbuch fur Hochfrequenztechnik" (Paperback for High Frequency Technology), 3rd Edition 1968, Page 496. These antennae combinations function as one individual antenna. In contrast to individual antennae, they have a higher gain and a changed radiation pattern with a tune-out in different directions.
It is not always possible or satisfactory to use antenna combinations of this type. In particular, if antennae of this type are to be used in mobile devices, such as vehicles, they can then, if at all, only be used in special cases as passive arrangements. The reason for this lies in the fact that the type of antenna combinations which are fitted to increase the gain, perform tune-outs. In conjunction with mobile devices, such as vehicles, however, it must be possible to receive signals with the vehicle aligned in any direction relative to the point of transmission. It is in fact fundamentally possible to track the receiving beams electronically in such cases. The costs as far as the wiring is concerned are, however, extremely high for this and in many cases cannot be justified.
When designing the structure of antennae on vehicles, special pre-requisites and rules apply, which mainly prevent the optimum dimensioning of the antennae with regard to the level of efficiency and the gain. The rod antenna, which is nowadays the most widely used, does in fact have a good level of efficiency but comes under criticism owing to its tendency for corrosion and damage and owing to its air resistance.
Alternatively, antennae integrated in the chassis, for example antennae in the rear windscreen, review mirror or bumper, have only a low level of efficiency particularly owing to the short distance to the metal in the chassis. This leads to noticeable losses in the reception quality, which can in fact be somewhat improved by the use of active antennae, but is, however, on the other hand associated with high costs as far as the wiring is concerned. In this case, it is nevertheless impossible to transmit with antennae of this type.